Multiple segment mold to manufacture tire bladders

ABSTRACT

A mold for forming a tire curing bladder. The mold has an outer mold assembly enclosing an inner mold core assembly. The outer mold comprises three sections and the inner mold comprises two portions. The outer mold and the inner mold core form a mold cavity therebetween. In one embodiment, the mold cavity defines a frog eye geometry where a cylindrical space is formed having a diameter that is greater for portions of the cylindrical spaced away from a centerline of the mold cavity than for portions near the centerline.

TECHNICAL FIELD OF THE INVENTION

The present invention is directed to a mold for forming bladders used inthe manufacture of tires, more particularly, but not exclusively, to amultiple segment mold for forming tire bladders having a generallycylindrical shape with top and bottom portions having a diametersomewhat larger than the central portion.

BACKGROUND OF THE INVENTION

Tire manufacturing generally involves two basic steps. The first step isbuilding the tire that is yet to be cured into what is termed a “greentire.” Commonly, a “green tire” is made by forming an inner liner andthen applying first and second plies or belts around the liner, and thenplacing a tread overtop the second ply. The second step is to cure thegreen tire in a tire curing press. The combination of these layersresults in a green tire ready for insertion into a tire curing press.The tire curing press includes a toroidally shaped mold that has thedesired tread imprinted along the inner toroidal interior space. Thegreen tire is placed inside of the tire curing press and a bladder isplaced inside of the green tire. When the bladder is inflated, the greentire is pressed against the inner surface of the tire mold, which isheated to melt and bond the different components of the green tiretogether.

The most common type of tire curing presses and bladders used areBag-O-Matic (B.O.M.) type. The bladders have a generally barrel shapewith a large empty area inside the center of the bladders, which allowsthe bladder ends to be clamped to a centerpost column inside of thecuring press. The centerpost column operates to stretch the bladders forinsertion into a green tire. Further, movement of the centerpost columnduring the curing process causes the bladders to bow outwards and usingsteam, water, or gas to inflate the bladder. In the traditional designof the tire curing bladders, the center section of the barrel is largerin diameter than the top and bottom sections of the barrel. Thesebladders are effective for forming tires having a generally roundinterior profile.

Tire bladders are fabricated in molds in which the bladder material,such as butyl rubber, is injected into a mold cavity and then allowed tocool. Although the design of bladder molds varies, they generallyincorporate a number of common features. The molds generally have outerand inner sections in which the outer section is split into top andbottom portions. After the bladder has been cured and cooled, the topportion of the outer section can be removed and the inner portion can beraised to remove the bladder from the mold. The existing molds are wellsuited for producing standard types of bladders having a center sectionthat is greater in diameter than the adjacent outer sections.

Currently, however, the demand for alternative types of tire designs isincreasing. A tire bladder having a profile known as a “frog eye” isgaining in popularity. A “frog eye” bladder is one where the diameter ofthe bladder is greater along the shoulder ends of the bladder than atthe center section. This configuration leads to a bulging of the upperand lower ends of the cylindrical barrel that generally resembles thebulging eyes of a frog.

The existing bladder molds suffer from many drawbacks in producing thesenew types of bladders. For example, the existing bladder molds aregenerally designed to produce a bladder having a center section with alarger diameter than the ends. In addition, the three component designof a two-part outer section and an essentially one-piece inner sectionof existing bladder molds are ill-suited to the manufacture of a bladderhaving the “frog eye” geometry.

Accordingly, there is need for an improved bladder mold for themanufacture of “frog eye” geometry bladders.

SUMMARY OF THE INVENTION

One aspect of the invention is directed to a tire curing bladder formingmold assembly. The tire curing bladder forming mold assembly iscomprised of an outer mold and an inner mold core. The outer mold is inturn comprised of removable and stackable top, middle and bottomsections. The removable top section rests upon the removable middlesection, which in turn, rests on the removable bottom section. The innermold core, which is enclosed within the outer mold, is comprised of twostackable portions; a removable inner mold core top portion which issupported on an inner mold core bottom portion. When assembled, theouter mold and the inner mold define a mold cavity having a centerlineand a diameter away from the centerline that is greater than thediameter at the centerline.

Another aspect of the invention is directed to a mold for fabricatingbladders having a diameter position spaced from the centerline of thebladder that is greater than the diameter of the bladder at thecenterline. The mold comprises a three component outer mold enclosing atwo component inner mold core. The outer mold and the inner mold coredefine a toroidal mold cavity therebetween having a larger diameter atthe upper and lower ends of the mold cavity than a diameter at acenterline of the mold cavity.

A further aspect of the invention is a method of forming a tire bladder.The bladder mold comprises an outer mold having top, middle, and bottomsections and an inner mold core having a top and bottom portion with theouter mold and inner mold core forming a mold cavity therebetween. Themethod comprises the steps of injecting material to form the tirebladder into the mold cavity, curing the material inside the bladdermold, raising a top mold section of the outer mold, lifting a top coreportion of the inner mold core, and raising a middle mold section of theouter mold. The method also includes the step of removing the formedtire curing bladder from the bottom portion of the inner mold core.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of a tire bladder forming moldaccording to one embodiment of the invention;

FIG. 1B illustrates the tire bladder forming mold of FIG. 1A aftermaterial has been injected therein to form a tire curing bladder;

FIG. 1C is an illustration of the cross-section of the tire bladderforming mold of FIG. 1B with the top section of the outer mold removed;

FIG. 1D is an illustration of the tire bladder forming mold of FIG. 1Cwith the top portion of the inner core mold removed;

FIG. 1E is an illustration of the tire bladder forming mold of FIG. 1Dwith the middle section of the outer mold removed;

FIG. 1F is an illustration of the tire bladder forming mold of FIG. 1Ewith the bottom portion of the inner core mold raised above the lowersection of the outer mold and the bladder expelled off from the innercore mold;

FIG. 2 illustrates a tire bladder formed using the tire bladder formingmold illustrated in FIGS. 1A through 1F;

FIG. 3 is a side elevational cross-sectional view of an alternativedesign of a tire bladder forming mold according to another embodiment ofthe invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 1A illustrates a mold 10 that fabricates bladders for use in a tirecuring process. The mold 10 generally comprises a three-sectional outermold 12 that encloses a two portion inner core mold 14. A toroidal moldcavity 16 is defined between the outer mold 12 and the inner core mold14 and has a centerline 17. The mold cavity 16 is filled with materialto fabricate a tire curing bladder during operation of the mold 10.After the bladder is formed inside the mold 10, portions of the outermold 12 are removed releasing the formed bladder from the inner coremold 14.

The outer mold 12 is comprised of three primary components; a topsection 18, a middle section 20, and a bottom section 22. The inner moldcore 14 is also further comprised of two primary components; a topportion 32 and a bottom portion 34 having a bulbous upper end 37integrally formed with a more narrow lower end 36. The top section 18 ofthe outer mold 12 overlies the inner mold core 14 and forms the outertop surface of the mold cavity 16 and a portion of the upper “frog eye”of the mold. An injection path 24 is formed in the top section 18 thatis in communication with the mold cavity 16 for injection of the bladdermaterial into the cavity during the molding process. The middle section20 of the outer mold 18 surrounds the majority of the upper end 37 ofthe bottom portion 34 of the inner mold core 14 and forms the outersurface of the majority of the mold cavity 16 that lies between the“frog eyes” of the mold. The bottom section 22 of the outer mold 18surrounds the lower end 36 of the bottom portion 34 of the inner mold14, underlies the bulbous upper end 36 of the bottom portion 34 andforms the outer bottom surface of the mold cavity and a portion of thelower “frog eye” of the mold. A locking mechanism 28 having a handle 30is inserted through an opening in the bottom section 22 to engage thelower end 36 of the bottom portion 34 of the inner mold 14 to hold theinner mold in position during the molding process as further describedbelow. The top section 18 rests on, and is releasably supported by, thelower section 22. The lower section 22 rests in an injection press orcan be supported by any appropriate structure.

The two primary components of the inner mold core 14 are stacked insidethe outer mold 12, with the top portion 32 resting on, and supported bythe bottom portion 34, which in turn rests on and is supported by apowered piston 45 (FIG. 1F). The top portion 32 forms the inside surfaceof the top surface of the mold cavity 16 and the inside surface of theupper “frog eye.” The upper bulbous end 37 of the bottom portion 34forms the remainder of the inside surface of the mold cavity 16.

The top portion 32 of the inner mold core 14 also has a removable handle38, attached to its top, shown in FIG. 1A in hidden lines, for use inmanually removing the top portion 32 after the tire bladder is formed.The lower end 36 of bottom portion 34 has an annular groove or one ormore notches 44 formed therein that cooperate with locking mechanism 28inserted through the bottom section 22 of outer mold 12 for holding thebottom portion 34 in position during the molding process. In addition,the lower end 36 also includes a cooperating first oil path 46, secondoil path 48, and oil tray 50 for providing heated oil to the interior 49of inner mold core 14 thereby heating the mold for forming/curing of thetire bladder. Accordingly, the multi-segmented inner core 14 cooperateswith the outer mold 12 to fabricate a tire curing bladder.

A blow off tube 42 is also formed in bottom portion 34. Followingformation of the tire bladder, and during the process of removing thefinished tire bladder from the mold 10 as detailed below, pressurizedair is introduced into the blow off tube 42 to inflate the tire bladderand, thereby, causing it to “blow off” the bottom portion 34.

Referring now to FIGS. 1A through 1F, the steps for forming a tirecuring bladder using mold 10 are illustrated. FIG. 1A shows theassembled mold 10, and illustrating the injection of material, such asbutyl rubber, into the mold cavity 14 through an injection path 24 bythe highlighted arrow 51. Following injection of the tire bladdermaterial, heated oil is introduced into the interior 49 of inner moldcore 14 to cause the mold to cure the bladder material as is well knownin the art. Referring now to FIG. 1B, the formed tire bladder 52 isshown in the mold cavity 16. The tire bladder includes protrusions 54that give the bladder 52 a cross-sectional shape with a smaller outerdiameter along the central portion 56 and a larger diameter at therespective ends 58. Accordingly, the bladder 52 possesses a distinctgeometry known to those skilled in the art as a “frog eye” bladder.Although the “frog eye” bladder has the largest diameters at the ends ofthe bladder, neither “frog eye” nor the present invention are limited tosuch a construction For example, a “frog eye” bladder can haveprotrusions located in other areas of the bladder besides the ends, andsuch a design is within the principles of the present invention.However, a “frog eye” bladder does not encompass a bladder that tapersfrom larger diameter to smaller diameter traveling from the centerlinetowards the ends of the bladder.

The process for removing the bladder 52 is illustrated in FIGS. 1C-1F.The process begins by removing the top section 18 of outer mold 12,which exposes the top portion 32 of the inner mold core 14 removablehandle 38 as best shown in FIG. 1C. In addition, the top of the bladder52 is also exposed. Referring now to FIG. 1D, the top portion 32 is thenremoved. In the illustrated embodiment, removal of the top portion 32occurs manually by lifting the top portion by the removable handle 38off of the bottom portion 34 of the inner mold core 14. Removal of theinner core upper portion 32 exposes additional portions of the bladder52.

Referring now to FIG. 1E, the middle section 20 of the outer mold 12 isremoved next. At this point almost the entire exterior surface of thebladder 52 is exposed and no longer restrained by the outer mold 12. Thebladder 52, however, remains adhered to the sides of the inner mold core14 and must be removed therefrom. As illustrated by FIG. 1F, the lockingmechanism 28 is retracted from notch 44 and the bottom portion 34 andbladder 52 are lifted out of the remaining bottom section 22 of theouter mold 12 by piston 45, thereby exposing the remainder of bladder52. Pressurized air is then introduced to central column 42 of bottomportion 34, which causes the tire bladder to inflate and be “blown off”the bottom portion 34 (i.e. be released from the bottom portion). Thetire bladder 52 can then be removed from the bottom portion 32, allowedto cool, and is trimmed and finished prior to sale to the ultimate user.

An example of a finished bladder 52 having an interior surface 60 andexterior surface 62 is shown in FIG. 2. The bladder 52 has a smallerdiameter throughout the central portion 56 of the bladder 52 proximal tothe centerline 64, and has a larger diameter at the ends of the bladder52 away from the centerline 60. Bladder 52 has many advantages over thetraditional B.O.M. bladders as described earlier.

FIG. 3 illustrates an alternative embodiment of a mold 66 of the presentinvention. The mold 66 includes an outer mold 68 and an inner mold core70, similar to the mold 10 illustrated in FIGS. 1A-1F. In addition, theouter mold 68 similarly has a top section 72, a middle section 74, and abottom 76 that are stackable and separable from one another as in theembodiment illustrated in FIGS. 1A-1F. The inner core 70, however, has atop portion 78 and a bottom portion 80 in which the top portion 78extends to about the centerline 81 of the mold cavity 88 rather thannear the top of the cavity. In this embodiment, the protrusions 82, 84are near the centerline 81 of the cavity 88 rather than at the ends. Thetop portion 78 forms one of the protrusions 82 and the other protrusion84 is formed by the bottom portion 80. Thus, a tire bladder 86 formedusing this alternative mold 66 has two protrusions near the center witha greater diameter than the rest of the tire curing bladder 86. Theouter mold 68 and the inner mold core 70 cooperate to form the moldcavity 88 for fabricating the bladder 86.

The invention has been described in the context of exemplaryembodiments. Those skilled in the art will appreciate that additions,deletions and modifications to the features described herein may be madewithout departing from the principles of the present invention. Forinstance, the inner core upper portion may be automatically removableinstead of manually removable. In addition, the use of hot oil inside ofthe inner core is optional and other types of fluids besides oil andother forms of heating can be used. Alternative systems for restrainingthe inner mold core besides the illustrated locking mechanism can alsobe used. Other modifications will be readily apparent to those skilledin this art. Accordingly, the following is claimed:

1. A tire curing bladder forming mold assembly comprising: an outer moldcomprising a plurality of stackable and movable sections, the outer moldincluding: a removable top section; a removable middle section forsupporting the removable top section when the plurality of sections arestacked; and a bottom section for supporting both the removable topsection and the removable middle section when the plurality of sectionsare stacked; and an inner mold core enclosed within the outer mold, theinner mold core comprising stackable portions, the inner mold including:a removable top portion; and a bottom portion for supporting theremovable top portion; the outer mold and inner mold core cooperating toform a mold cavity therebetween having a centerline, the mold cavityhaving a diameter away from the centerline thereof that is greater thanthe diameter at the centerline.
 2. The mold of claim 1 wherein the moldcavity has a diameter at symmetric locations spaced from the centerlineof the mold cavity greater than the diameter at the centerline of themold cavity.
 3. The mold of claim 1 wherein the mold cavity has a topand a bottom, the diameter of the mold cavity at the top and bottombeing greater than the diameter of the centerline of the mold cavity. 4.The mold of claim 1, wherein the removable top section of the outer moldis adapted to be vertically removed from the outer mold.
 5. The mold ofclaim 1, wherein the removable top portion of the inner mold core isadapted to be manually removed.
 6. The mold of claim 1, wherein thebottom portion of the inner mold core is adapted to be raised above thebottom section of the outer mold by a power piston.
 7. A mold forfabricating bladders having a diameter at a position spaced from thecenterline of the bladder that is greater than the diameter of thebladder at the centerline comprising: a three component outer mold; atwo component inner mold core enclosed by said outer mold; the outermold and the inner mold core defining a mold cavity therebetween,wherein the mold cavity has a generally torodial shape having a largerdiameter at the upper and lower ends of the mold cavity than a diameterat a centerline of the mold cavity.
 8. The mold of claim 7 wherein thethree component outer mold includes a removable top section, a removablemiddle section for supporting the removable top section duringfabrication of a bladder, and a bottom section for supporting both theremovable top section and the removable middle section duringfabrication of a bladder.
 9. The mold of claim 7 wherein thetwo-component inner mold core includes a removable top portion and abottom portion.
 10. The mold of claim 9 wherein the removable topportion of the inner mold core is adapted to be manually removed. 11.The mold of claim 9 wherein the bottom portion includes a channel fortransmitting pressurized air.